Upgrade of the CO₂ Direct Absorption Method for Low-Level ¹⁴C Liquid Scintillation Counting

Abstract

A new system for CO 2 absorption and liquid scintillation counting (LSC) was designed and developed along with its inherent measurement protocol for radiocarbon analysis in gaseous emissions, fuels, and biobased products. CO 2 is chemically trapped as a carbamate in a suitable absorbing solution (3-methoxy-propyl-amine), gravimetrically measured, and analyzed by LSC (using a Quantulus TM 1220) to determine the 14 C content. The use of cryogenic traps and a pressure transducer in the system prevents the need for closed-loop recirculation or additional steps to maximize CO 2 capture in a short amount of time. The choice of PTFE vials used both for CO 2 pretreatment and subsequent LSC analysis provides the opportunity to significantly reduce the background counting down to 40% with respect to the low- 40 K glass vials. This upgrade resulted in improving the maximum detectable age back to 36,000 yr BP in routine measurements. This method therefore turns out to be flexible enough to be applied for 14 C dating as well as to differentiate between modern and fossil carbon.